Corrugated drainage pipe with staggered arrangement of rib interruptions

ABSTRACT

A resilient plastic drainage pipe of lightweight construction having spaced apart successively arranged annular ribs with interconnecting annular valley portions therebetween defining corrugations along the periphery of the pipe, the ribs being arranged in successive groups with each of the successive groups of ribs having at least several of the ribs interrupted by recessed wall portions, and with a drainage hole being provided in each of the recessed wall portions of the interrupted ribs. The recessed wall portions in each group of ribs are arcuately spaced from one another at three arcuate locations in the lower half of the pipe with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations. Additionally, sight means is provided on the outer surface of the pipe extending longitudinally thereof and located in diametrically opposed relation to the middle location of the arcuately spaced drainage holes in the pipe, the sight means being thereby adapted for visually aiding in installing the pipe in the ground with all of the drainage holes located below the horizontal center line of the pipe and with the middle drainage holes occupying the lowermost position.

United States Patent [1 1 Maroschak [451 Jan. 21, 1975 CORRUGATED DRAINAGE PIPE WITH STAGGERED ARRANGEMENT OF RIB INTERRUPTIONS [76] Inventor: Ernest J. Maroschak, Box 878,

Roseboro, NC. 28382 [22] Filed: July 19, 1973 [21] Appl. No.: 380,905

Related U.S. Application Data [63] Continuation-impart of Ser. No. 228,508, Feb. 23,

1972, Pat. No. 3,802,202.

[52] U.S. Cl 61/11, 61/72.1, 138/121, 138/173 [51] Int. Cl E02b 11/00, F16] 11/12 [58] Field of Search ..61/11,10, 12,13, 72.1; 138/122,121,173,178,172

[56] References Cited UNITED STATES PATENTS 3,658,097 4/1972 Martin et a1. 138/121 OTHER PUBLICATIONS Sweets File Cat., 15.21/l-Ian 61-12, pub. 1970.

Primary Examiner-Jacob Shapiro Attorney, Agent, or Firm-Parrott, Bell, Seltzer, Park & Gibson [57] ABSTRACT A resilient plastic drainage pipe of lightweight construction having spaced apart successively arranged annular ribs with interconnecting annular valley portions therebetween defining corrugations along the pcriphery of the pipe, the ribs being arranged in successive groups with each of the successive groups of ribs having at least several of the ribs interrupted by recessed wall portions, and with a drainage hole being provided in each of the recessed wall portions of the interrupted ribs. The recessed wall portions in each group of ribs are arcuately spaced from one another at three arcuate locations in the lower half of the pipe with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations. Additionally, sight means is provided on the outer surface of the pipe extending longitudinally thereof and located in diametrically opposed relation to the middle location of the arcuately spaced drainage holes in the pipe, the sight means being thereby adapted for visually aiding in installing the pipe in the ground with all of the drainage holes located below the horizontal center line of the pipe and with the middle drainage holes occupying the lowermost position.

15 Claims, 7 Drawing Figures CORRUGATED DRAINAGE PIPE WITH STAGGERED ARRANGEMENT OF RIB INTERRUPTIONS This application is a continuation-in-part of my copending application Ser. No. 228,508, filed Feb. 23, 1972, now US. Pat. No. 3,802,202, entitled CORRU- GATED DRAINAGE PIPE.

This invention relates to resilient plastic corrugated drainage pipes and it is an object of this invention to provide an improved drainage pipe of lightweight construction particularly adapted for use in septic tanks.

In my earlier copending application Ser. No. 228,508, filed Feb. 23, 1972, a corrugated plastic drainage pipe is disclosed wherein certain of the ribs of the pipe are interrupted and include a set of three circularly arranged spaced apart rib segments with recessed wall portions interconnecting the three rib segments, and wherein drainage holes are provided in each of the recessed wall portions between the rib segments. The rib segments are so arranged as to position the drainage holes around the bottom of the pipe so as to allow liquids to drain from the pipe. The present invention differs over my earlier copending application by providing the recessed wall portions in groups in arcuately spaced and longitudinally staggered relation so that at least one of the recessed wall portions in each group is longitudinally spaced from other recesses in the same group.

The longitudinally staggered, arcuately spaced arrangement of the recesses in accordance with the present invention provides several benefits over the arrangement disclosed in my earlier copending application, as for example, facilitating drilling the drainage holes in the pipe, since the drilling machines for forming the drainage holes in the pipe may be staggered longitudinally from one another. Additionally, since the drainage holes are distributed along the length of the pipe rather than being grouped in a common rib, liquids may drain from the pipe more evenly along its length rather than from clustered locations along the pipe as in my earlier application. Finally, the compressive strength of the pipe is improved, since the drainage holes and the recessed wall portions or interruptions in the ribs, which inherently form somewhat weaker areas in the walls of the pipe than the uninterrupted portions thereof, are distributed over the length of the pipe rather than being concentrated in selected ribs thereof.

In view of the foregoing, it is a more specific object of this invention to provide an improved corrugated resilient plastic pipe having recessed wall portions provided in the ribs thereof in arcuately spaced and longitudinally staggered relation along the length of the pipe.

Some of the objects and advantages of the invention having been stated, others will appear as the description proceeds when taken in connection with the accompanying drawings, in which FIG. 1 is a bottom plan view of a length of corrugated drainage pipe in accordance with one form of the present invention, showing the drainage holes in the underside thereof;

FIG. 2 is a vertical sectional view of the drainage pipe taken along theline 22 of FIG. 1, and shown with the pipe in its normal orientation with the drainage holes in the lower half thereof;

FIG. 3 is a vertical sectional view similar to FIG. 2

but taken along the line 3-3 of FIG. 1;

FIG. 4 is a bottom plan view ofa length of corrugated drainage pipe in accordance with a second form of this invention, showing the drainage holes in the underside thereof;

FIG. 5 is a vertical sectional view of the drainage pipe taken along the line 5-5 of FIG. 4 and shown with the pipe in its normal orientation with the drainage holes in the lower half thereof;

FIG. 6 is a vertical sectional view similar to FIG. 5 but taken along the line 6-6 of FIG. 4; and

FIG. 7 is a vertical sectional view similar to FIG. 5 but taken along the line 7-7 of FIG. 4.

Referring now to the first form of the invention, as illustrated in FIGS. 1-3, reference numeral 10 broadly indicates a corrugated drainage pipe in accordance with this invention which is formed of a plastic material such'as polyethylene, with the wall thickness thereof preferably being no greater than about 1/ 16 inch to provide a pipe of lightweight construction.

Successively arranged ribs 11 with interconnecting valley portions 12 therebetween define annular corrugations along the periphery of the pipe, with the ribs 11 being somewhat wider than the valley portions 12 and being provided with side wall portions 11a which connect with the valley portions 12. As illustrated, the ribs are arranged in successive groups of six ribs with two of the ribs in each group being interrupted by arcuately elongate recessed wall portions 20 and with the remaining four ribs in the group being uninterrupted and located in pairs between successive interrupted ribs.

It will be noted from FIG. 1 that two types of interrupted ribs are provided, with alternate ones of the interrupted ribs, broadly designated at 13, having a single recessed wall portion 20 therein and having an elongate arcuate rib segment 14 forming the remaining portion of the interrupted rib l3, and with the remaining interrupted ribs, designated at 15, having two arcuately spaced recessed wall portions 20 therein with a relatively long arcuate rib segment 16 and a relatively short arcuate rib segment 17 interconnecting the two recessed wall portions and forming the remaining portions of the interrupted rib 15.

As illustrated, each of the arcuately elongate recessed wall portions 20 are positioned at substantially the same level as immediately adjacent valley portions 12, with end walls 21 at opposite ends of the recessed wall portions 20 extending outwardly and defining the arcuate extent of the interruptions in the interrupted ribs and serving to provide compressive strength to the adjacent rib segments.

As illustrated, the pipe is adapted for being used for drainage purposes, as for example in a septic tank field, and a drainage hole 23 is provided through each of the recessed wall portions 20 in the pipe to permit liquids to flow from the pipe. However, since corrugated plastic pipe is also conventionally used for various purposes without drainage holes therein, it may in some instances be economically desirable to omit the drainage holes from the recessed wall portions 20 and to thereby employ the same molding apparatus and mold block for forming solid or unperforated pipe as for forming drainage pipe having holes therein.

When the pipe is to be employed for drainage purposes, the holes provided therein are desirably of at least a inch diameter, and preferably about 34 inch diameter to permit liquids to freely drain from the pipe. By locating the drainage holes through the recessed wall portions of the pipe between adjacent rib segments and substantially at the level of adjacent valley portions 12, the drainage holes are spaced inwardly from the periphery of the ribs and away from the surrounding soil when installed underground, which further facilitates the drainage of liquids from the pipe.

Throughout the length of the pipe, the interrupted ribs 13, in the successive groups of ribs are correspondingly arranged so as to position the respective recessed wall portions in longitudinally aligned rows at three arcuately spaced locations in the same half of the pipe. As seen in FIG. 1, the recessed wall portions 20 in successive interrupted ribs 13 are located at the middle or innermost location of the three arcuately spaced locations, with the two arcuately spaced recessed wall portions 20 in successive interrupted ribs 15 being located in longitudinally offset, arcuately spaced relation on opposite sides thereof in the outermost of the three arcuately spaced locations.

When the drainage pipe is properly installed in the ground, the drainage holes 23 are located in the lower half of the pipe to permit drainage of liquids therefrom into the earth below. For visually aiding in installing the pipe in the ground with the drainage holes properly oriented lowermost, sight means (FIGS. 2 and 3) is preferably provided extending longitudinally of the pipe in diametrically opposed relation to the drainage hole in the interrupted ribs 13, which as previously noted, is in the middle or innermost of the three arcuately spaced locations. As illustrated, sight means 30 is in the form of a painted line contrasting with the color of the drainage pipe and extending on and along the outer surface of the annular ribs. Sight means 30 may, however, if desired, be in the form of a series of small rib portions extending longitudinally of the pipe along the outer surface of the ribs.

Referring more particularly to interrupted rib l5, rib segment 16 thereof, as noted earlier, is of greater arcuate extent than the other rib segment 17. Rib segment 16 desirably has an arcuate extent encompassing at least the upper half of the drainage pipe, i.e., at least 180 degrees, and preferably has an extent of at least 200 to 220 degrees so as to shieldingly protect the two drainage holes 23 during the backfilling of earth around the drainage pipe to avoid blocking the holes. As illustrated (FIG. 2), the intersecting axes of the arcuately spaced holes in interrupted rib 15 define an included angle of about 120 degrees (angle A), with each drainage hole also being arcuately spaced about 120 degrees from the top of the pipe where sight means 30 is located.

Each elongate recessed wall portion preferably has an arcuate extent of about -50 degrees to provide sufficient room for drilling drainage holes 23 therein, which as illustrated, encompass an arcuate extent of about 15 to 25 degrees and are preferably centered in the elongate recessed wall portions. The additional arcuate extent of the elongate recessed wall portions serves to provide a degree of tolerance for minor misalignment of the pipe with respect to the drilling apparatus during the drilling operation.

Referring to interrupted rib 13, it will be noted that the recessed wall portion 20 thereof has an arcuate extent similar to that of the recesses in interrupted rib 15, with arcuate rib segment 14 comprising the remaining portion of the interrupted rib. As illustrated, drainage hole 23 in rib 15 is located lowermost in the pipe about 180 degrees from the top of the pipe where sight means 30 is located. Thus, as illustrated in FIG. 1, the drainage holes in the pipe collectively cover an arcuate extent of about degrees in the lower portion of the pipe and form three longitudinally aligned rows of drainage holes, which rows are arcuately spaced about 60 degrees apart from each other.

The second form of the invention, as illustrated in FIGS. 4-7, is similar to the first form illustrated in FIGS. I3, and the same reference numerals have been employed for like elements where applicable, except that the three interrupted ribs in each group of six ribs are identified by the reference numerals 40, 42 and 44 respectively.

Referring to FIG. 4, it will be noted that the ribs 11 are arranged in successive groups of six ribs with three of the ribs in each group (40, 42, 44) being interrupted by a recessed wall portion 20, and with the remaining three ribs in each group being uninterrupted and located between successive interrupted ribs. The recessed wall portion in each of the interrupted ribs 40, 42, 44 has an arcuate extent of about 35-50 degrees, with elongate arcuate rib segments 41, 43, 45 respectively, comprising the remaining portions of the respective interrupted ribs.

As in the first form of the invention, the interrupted ribs (40, 42, 44) in successive groups of ribs are correspondingly arranged throughout the length of the pipe so as to position the respective recessed wall portions in three longitudinally aligned rows at three arcuately spaced locations in the same half of the pipe. The recessed wall portion in interrupted rib 42 is located at the middle or lowermost location of the three arcuate locations, with the recessed wall portion in interrupted rib-40 being located on one side thereof, and with the recessed wall portions in interrupted rib 44 being located on the opposite side thereof. Sight means 30 is also preferably provided in diamterically opposed relation to the drainage holes in interrupted rib 42 for visually aiding in installing the pipe in the ground with the drainage holes properly positioned lowermost.

As illustrated, the drainage hole in interrupted rib 40 is located in the recessed wall portion 20 on one side of the pipe and arcuately spaced about 120 degrees from the top of the pipe where sight means 30 is located (angle B in FIG. 5), while the drainage hole in interrupted rib 44 is located in the recessed wall portion 20 on the opposite side of the pipe and also spaced about 120 degrees from the top of the pipe (angle C in FIG. 7). As previously noted, the drainage hole in interrupted rib 42 is positioned in diametrically opposed relation to sight means 30 at the top of the pipe.

Thus, as seen in FIG. 4, the drainage holes collectively cover an arcuate extent of about 120 degrees in the lower portion of the pipe and form three longitudinally aligned rows of holes which are arcuately spaced about 60 degrees apart from each other.

It will be noted that in both of the illustrated forms of this invention, at least one of the drainage holes in each group of ribs is in longitudinally offset or staggered relation with respect to another drainage hole in the group with no two drainage holes being positioned closely adjacent one another in the same rib. Thus, the inherent weaknesses in the wall of the pipe formed by the drainage holes and the recessed wall portions are distributed throughout the length of the pipe rather than being concentrated in a single rib as in my aforementioned earlier-filed copending application. It should be apparent from the foregoing that the instant invention thus provides a corrugated plastic drainage pipe of enhanced compressive strength as compared to my earlier invention disclosed in the aforementioned copending application.

In the drawings and specification there have been set forth preferred embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

That which is claimed is:

l. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, and with a drainage hole being provided in each of the recessed wall portions of the interrupted ribs, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe, and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, at least one of the recessed wall portions in each group of ribs being offset longitudinally of the pipe from a recessed wall portion in another rib of the group, and wherein sight means is provided on the outer surface of said pipe extending longitudinally thereof and located in diametrically opposed relation to the middle location of the arcuately spaced drainage holes in the pipe, said sight means being thereby adapted for visually aiding in installing the pipe in the ground with all of the drainage holes located below the horizontal center line of the pipe and with the middle drainage holes occupying the lowermost position.

2. A resilient plastic pipe according to claim 1 wherein at least one uninterrupted rib is positioned between adjacent interrupted ribs throughout the pipe.

3. A resilient plastic pipe according to claim 1 wherein said recessed wall portions are positioned substantially at the level of adjacent valley portions.

4. A resilient plastic pipe according to claim 1, wherein the drainage holes in each group of ribs are arcuately spaced from each other about 60 degrees apart.

5. A resilient plastic pipe according to claim 1, wherein each group of ribs includes two longitudinally spaced interrupted ribs with a pair of uninterrupted ribs being provided therebetween, and wherein two of the elongate recesses in each group of ribs are positioned in a common interrupted rib in arcuately spaced relation in the outermost of said three arcuate locations, with the third elongate recess being positioned in the other interrupted rib and located in the middle of said three arcuate locations.

6. A resilient plastic pipe according to claim 1, wherein each group of ribs includes three interrupted ribs with an uninterrupted rib being provided between adjacent interrupted ribs, and wherein each of the three interrupted ribs has one of said elongate recesses provided therein with said recesses being located respectively at said three different arcuate locations on the pipe.

7. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions and with at least one uninterrupted rib positioned between adjacent interrupted ribs throughout the pipe, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, at least one of the recessed wall portions in each group of ribs being offset longitudinally of the pipe from a recessed wall portion in another rib of the group, a drainage hole provided in each of the recessed wall portions of the interrupted ribs with the drainage holes in each group of ribs being arcuately spaced from each other about 60 degrees apart, and sight means provided on the outer surface of said pipe extending longitudinally thereof and located in diametrically opposed relation to the middle location of the arcuately spaced drainage holes in the pipe, said sight means being thereby adapted for visually aiding in installing the pipe in the ground with all of the drainage holes located below the horizontal center line of the pipe and with the middle drainage holes occupying the lowermost position.

8. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions and with at least one uninterrupted rib positioned between adjacent interrupted ribs throughout the pipe, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, and a drainage hole provided in each of the recessed wall portions in each group of ribs, and wherein at least one of the recessed wall portions in each group of ribs is offset longitudinally of the pipe from a recessed wall portion in another rib of the group.

9. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, wherein the respective recessed wall portions in each group of ribs are arcuately spaced from one another with at least one of the recessed wall portions being offset longitudinally of the pipe from a recessed wall portion in another rib of the group, a drainage hole being provided in each of the recessed wall portions in each group of ribs, and wherein at least one uninterrupted rib is positioned between adjacent interrupted ribs throughout the pipe.

10. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, and wherein the respective recessed wall portions in each group of ribs are arcuately spaced from one another with at least one of the recessed wall portions being offset longitudinally of the pipe from a recessed wall portion in another rib of the group.

11. A resilient plastic pipe according to claim 10 wherein two of the recessed wall portions in each group of ribs are located in a common interrupted rib and wherein the remaining recessed wall portion in each group of ribs are offset longitudinally of the pipe from said common interrupted rib.

12. A resilient plastic pipe according to claim 10, wherein the respective recessed wall portions in each group of ribs are each offset longitudinally of the pipe from one another.

13. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe, and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, and wherein at least one of the recessed wall portions in each group of ribs is offset longitudinally of the pipe from a recessed wall portion in another rib of the group.

14. A resilient plastic pipe according to claim 13, wherein each group of ribs includes two longitudinally spaced interrupted ribs with a pair of uninterrupted ribs being provided therebetween, and wherein two of the recessed wall portions in each group of ribs are positioned in a common interrupted rib in arcuately spaced relation in the outermost of said three arcuate locations, with the third recessed wall portion being positioned in the other interrupted rib and located in the middle of said three arcuate locations.

15. A resilient plastic pipe according to claim 13, wherein each group of ribs includes three interrupted ribs with an uninterrupted rib being provided between adjacent interrupted ribs, and wherein each of the three interrupted ribs has one of said recessed wall portions provided therein with said recessed wall portions being located respectively at said three different arcuate locations on the pipe. 

1. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, and with a drainage hole being provided in each of the recessed wall portions of the interrupted ribs, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe, and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, at least one of the recessed wall portions in each group of ribs being offset longitudinally of the pipe from a recessed wall portion in another rib of the group, and wherein sight means is provided on the outer surface of said pipe extending longitudinally thereof and located in diametrically opposed relation to the middle location of the arcuately spaced drainage holes in the pipe, said sight means being thereby adapted for visually aiding in installing the pipe in the ground with all of the drainage holes located below the horizontal center line of the pipe and with the middle drainage holes occupying the lowermost position.
 2. A resilient plastic pipe according to claim 1 wherein at least one uninterrupted rib is positioned between adjacent interrupted ribs throughout the pipe.
 3. A resilient plastic pipe according to claim 1 wherein said recessed wall portions are positioned substantially at the level of adjacent valley portions.
 4. A resilient plastic pipe according to claim 1, wherein the drainage holes in each group of ribs are arcuately spaced from each other about 60 degrees apart.
 5. A resilient plastic pipe according to claim 1, wherein each group of ribs includes two longitudinally spaced interrupted ribs with a pair of uninterrupted ribs being provided therebetween, and wherein two of the elongate recesses in each group of ribs are positioned in a common interrupted rib in arcuately spaced relation in the outermost of said three arcuate locations, with the third elongate recess being positioned in the other interrupted rib and located in the middle of said three arcuate locations.
 6. A resilient plastic pipe according to claim 1, wherein each group of ribs includes three interrupted ribs with an uninterrupted rib being provided between adjacent interrupted ribs, and wherein each of the three interrupted ribs has one of said elongate recesses provided therein with said recesses being located respectively at said three different arcuate locations on the pipe.
 7. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions and with at least one uninterrupted rib positioned between adjacent interrupted ribs throughout the pipe, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, at least one of the recessed wall portions in each group of ribs being offset longitudinally of the pipe from a recessed wall portion in another rib of the group, a drainage hole provided in eacH of the recessed wall portions of the interrupted ribs with the drainage holes in each group of ribs being arcuately spaced from each other about 60 degrees apart, and sight means provided on the outer surface of said pipe extending longitudinally thereof and located in diametrically opposed relation to the middle location of the arcuately spaced drainage holes in the pipe, said sight means being thereby adapted for visually aiding in installing the pipe in the ground with all of the drainage holes located below the horizontal center line of the pipe and with the middle drainage holes occupying the lowermost position.
 8. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions and with at least one uninterrupted rib positioned between adjacent interrupted ribs throughout the pipe, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe and with the recessed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, and a drainage hole provided in each of the recessed wall portions in each group of ribs, and wherein at least one of the recessed wall portions in each group of ribs is offset longitudinally of the pipe from a recessed wall portion in another rib of the group.
 9. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, wherein the respective recessed wall portions in each group of ribs are arcuately spaced from one another with at least one of the recessed wall portions being offset longitudinally of the pipe from a recessed wall portion in another rib of the group, a drainage hole being provided in each of the recessed wall portions in each group of ribs, and wherein at least one uninterrupted rib is positioned between adjacent interrupted ribs throughout the pipe.
 10. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, and wherein the respective recessed wall portions in each group of ribs are arcuately spaced from one another with at least one of the recessed wall portions being offset longitudinally of the pipe from a recessed wall portion in another rib of the group.
 11. A resilient plastic pipe according to claim 10 wherein two of the recessed wall portions in each group of ribs are located in a common interrupted rib and wherein the remaining recessed wall portion in each group of ribs are offset longitudinally of the pipe from said common interrupted rib.
 12. A resilient plastic pipe according to claim 10, wherein the respective recessed wall portions in each group of ribs are each offset longitudinally of the pipe from one another.
 13. A resilient plastic pipe having spaced apart successive annular ribs with annular valley portions therebetween defining corrugations along the periphery of the pipe, said ribs being arranged in successive groups with each of the successive groups of ribs having at least several ribs in the group interrupted by recessed wall portions, the recessed wall portions in each group of ribs being three in number and being arcuately spaced apart from each other at three arcuate locations in the lower half of the pipe, and with the receSsed wall portions in adjacent groups of ribs being positioned in similar arcuate locations, and wherein at least one of the recessed wall portions in each group of ribs is offset longitudinally of the pipe from a recessed wall portion in another rib of the group.
 14. A resilient plastic pipe according to claim 13, wherein each group of ribs includes two longitudinally spaced interrupted ribs with a pair of uninterrupted ribs being provided therebetween, and wherein two of the recessed wall portions in each group of ribs are positioned in a common interrupted rib in arcuately spaced relation in the outermost of said three arcuate locations, with the third recessed wall portion being positioned in the other interrupted rib and located in the middle of said three arcuate locations.
 15. A resilient plastic pipe according to claim 13, wherein each group of ribs includes three interrupted ribs with an uninterrupted rib being provided between adjacent interrupted ribs, and wherein each of the three interrupted ribs has one of said recessed wall portions provided therein with said recessed wall portions being located respectively at said three different arcuate locations on the pipe. 